<?php
/**
 * Zend Framework
 *
 * LICENSE
 *
 * This source file is subject to the new BSD license that is bundled
 * with this package in the file LICENSE.txt.
 * It is also available through the world-wide-web at this URL:
 * http://framework.zend.com/license/new-bsd
 * If you did not receive a copy of the license and are unable to
 * obtain it through the world-wide-web, please send an email
 * to license@zend.com so we can send you a copy immediately.
 *
 * @category   Zend
 * @package    Zend_Search_Lucene
 * @copyright  Copyright (c) 2005-2009 Zend Technologies USA Inc. (http://www.zend.com)
 * @license    http://framework.zend.com/license/new-bsd     New BSD License
 * @version    $Id: LockManager.php 16971 2009-07-22 18:05:45Z mikaelkael $
 */

/** Zend_Search_Lucene_Storage_Directory */
require_once 'Zend/Search/Lucene/Storage/Directory.php';

/** Zend_Search_Lucene_Storage_File */
require_once 'Zend/Search/Lucene/Storage/File.php';

/**
 * This is an utility class which provides index locks processing functionality
 *
 * @category   Zend
 * @package    Zend_Search_Lucene
 * @copyright  Copyright (c) 2005-2009 Zend Technologies USA Inc. (http://www.zend.com)
 * @license    http://framework.zend.com/license/new-bsd     New BSD License
 */
class Zend_Search_Lucene_LockManager
{
	/**
	 * consts for name of file to show lock status
	 */
	const WRITE_LOCK_FILE                = 'write.lock.file';
	const READ_LOCK_FILE                 = 'read.lock.file';
	const READ_LOCK_PROCESSING_LOCK_FILE = 'read-lock-processing.lock.file';
	const OPTIMIZATION_LOCK_FILE         = 'optimization.lock.file';

	/**
	 * Obtain exclusive write lock on the index
	 *
	 * @param Zend_Search_Lucene_Storage_Directory $lockDirectory
	 * @return Zend_Search_Lucene_Storage_File
	 * @throws Zend_Search_Lucene_Exception
	 */
	public static function obtainWriteLock(Zend_Search_Lucene_Storage_Directory $lockDirectory)
	{
		$lock = $lockDirectory->createFile(self::WRITE_LOCK_FILE);
		if (!$lock->lock(LOCK_EX)) {
			require_once 'Zend/Search/Lucene/Exception.php';
			throw new Zend_Search_Lucene_Exception('Can\'t obtain exclusive index lock');
		}
		return $lock;
	}

	/**
	 * Release exclusive write lock
	 *
	 * @param Zend_Search_Lucene_Storage_Directory $lockDirectory
	 */
	public static function releaseWriteLock(Zend_Search_Lucene_Storage_Directory $lockDirectory)
	{
		$lock = $lockDirectory->getFileObject(self::WRITE_LOCK_FILE);
		$lock->unlock();
	}

	/**
	 * Obtain the exclusive "read escalation/de-escalation" lock
	 *
	 * Required to protect the escalate/de-escalate read lock process
	 * on GFS (and potentially other) mounted filesystems.
	 *
	 * Why we need this:
	 *  While GFS supports cluster-wide locking via flock(), it's
	 *  implementation isn't quite what it should be.  The locking
	 *  semantics that work consistently on a local filesystem tend to
	 *  fail on GFS mounted filesystems.  This appears to be a design defect
	 *  in the implementation of GFS.  How this manifests itself is that
	 *  conditional promotion of a shared lock to exclusive will always
	 *  fail, lock release requests are honored but not immediately
	 *  processed (causing erratic failures of subsequent conditional
	 *  requests) and the releasing of the exclusive lock before the
	 *  shared lock is set when a lock is demoted (which can open a window
	 *  of opportunity for another process to gain an exclusive lock when
	 *  it shoudln't be allowed to).
	 *
	 * @param Zend_Search_Lucene_Storage_Directory $lockDirectory
	 * @return Zend_Search_Lucene_Storage_File
	 * @throws Zend_Search_Lucene_Exception
	 */
	private static function _startReadLockProcessing(Zend_Search_Lucene_Storage_Directory $lockDirectory)
	{
		$lock = $lockDirectory->createFile(self::READ_LOCK_PROCESSING_LOCK_FILE);
		if (!$lock->lock(LOCK_EX)) {
			require_once 'Zend/Search/Lucene/Exception.php';
			throw new Zend_Search_Lucene_Exception('Can\'t obtain exclusive lock for the read lock processing file');
		}
		return $lock;
	}

	/**
	 * Release the exclusive "read escalation/de-escalation" lock
	 *
	 * Required to protect the escalate/de-escalate read lock process
	 * on GFS (and potentially other) mounted filesystems.
	 *
	 * @param Zend_Search_Lucene_Storage_Directory $lockDirectory
	 */
	private static function _stopReadLockProcessing(Zend_Search_Lucene_Storage_Directory $lockDirectory)
	{
		$lock = $lockDirectory->getFileObject(self::READ_LOCK_PROCESSING_LOCK_FILE);
		$lock->unlock();
	}


	/**
	 * Obtain shared read lock on the index
	 *
	 * It doesn't block other read or update processes, but prevent index from the premature cleaning-up
	 *
	 * @param Zend_Search_Lucene_Storage_Directory $defaultLockDirectory
	 * @return Zend_Search_Lucene_Storage_File
	 * @throws Zend_Search_Lucene_Exception
	 */
	public static function obtainReadLock(Zend_Search_Lucene_Storage_Directory $lockDirectory)
	{
		$lock = $lockDirectory->createFile(self::READ_LOCK_FILE);
		if (!$lock->lock(LOCK_SH)) {
			require_once 'Zend/Search/Lucene/Exception.php';
			throw new Zend_Search_Lucene_Exception('Can\'t obtain shared reading index lock');
		}
		return $lock;
	}

	/**
	 * Release shared read lock
	 *
	 * @param Zend_Search_Lucene_Storage_Directory $lockDirectory
	 */
	public static function releaseReadLock(Zend_Search_Lucene_Storage_Directory $lockDirectory)
	{
		$lock = $lockDirectory->getFileObject(self::READ_LOCK_FILE);
		$lock->unlock();
	}

	/**
	 * Escalate Read lock to exclusive level
	 *
	 * @param Zend_Search_Lucene_Storage_Directory $lockDirectory
	 * @return boolean
	 */
	public static function escalateReadLock(Zend_Search_Lucene_Storage_Directory $lockDirectory)
	{
		self::_startReadLockProcessing($lockDirectory);

		$lock = $lockDirectory->getFileObject(self::READ_LOCK_FILE);

		// First, release the shared lock for the benefit of GFS since
		// it will fail the conditional request to promote the lock to
		// "exclusive" while the shared lock is held (even when we are
		// the only holder).
		$lock->unlock();

		// GFS is really poor.  While the above "unlock" returns, GFS
		// doesn't clean up it's tables right away (which will potentially
		// cause the conditional locking for the "exclusive" lock to fail.
		// We will retry the conditional lock request several times on a
		// failure to get past this.  The performance hit is negligible
		// in the grand scheme of things and only will occur with GFS
		// filesystems or if another local process has the shared lock
		// on local filesystems.
		for ($retries = 0; $retries < 10; $retries++) {
			if ($lock->lock(LOCK_EX, true)) {
				// Exclusive lock is obtained!
				self::_stopReadLockProcessing($lockDirectory);
				return true;
			}

			// wait 1 microsecond
			usleep(1);
		}

		// Restore lock state
		$lock->lock(LOCK_SH);

		self::_stopReadLockProcessing($lockDirectory);
		return false;
	}

	/**
	 * De-escalate Read lock to shared level
	 *
	 * @param Zend_Search_Lucene_Storage_Directory $lockDirectory
	 */
	public static function deEscalateReadLock(Zend_Search_Lucene_Storage_Directory $lockDirectory)
	{
		$lock = $lockDirectory->getFileObject(self::READ_LOCK_FILE);
		$lock->lock(LOCK_SH);
	}

	/**
	 * Obtain exclusive optimization lock on the index
	 *
	 * Returns lock object on success and false otherwise (doesn't block execution)
	 *
	 * @param Zend_Search_Lucene_Storage_Directory $lockDirectory
	 * @return mixed
	 */
	public static function obtainOptimizationLock(Zend_Search_Lucene_Storage_Directory $lockDirectory)
	{
		$lock = $lockDirectory->createFile(self::OPTIMIZATION_LOCK_FILE);
		if (!$lock->lock(LOCK_EX, true)) {
			return false;
		}
		return $lock;
	}

	/**
	 * Release exclusive optimization lock
	 *
	 * @param Zend_Search_Lucene_Storage_Directory $lockDirectory
	 */
	public static function releaseOptimizationLock(Zend_Search_Lucene_Storage_Directory $lockDirectory)
	{
		$lock = $lockDirectory->getFileObject(self::OPTIMIZATION_LOCK_FILE);
		$lock->unlock();
	}

}
